Cool idea but maybe a marketing gimmick? This is Chuck's expertise but according to the specs: The design architecture of the Valvebucker circuit is noteworthy, making use of sweet spots found from outside the typical operational points of vacuum tubes, by using relatively low voltages,” Ruokangas writes.
I may be wrong but I don't think voltage starved, tube pre-amps sound as good as the high-voltage tube circuits but if you used a high voltage tube preamp it would be too hot to contain the heat inside of a bass or guitar.
My internet friend here in Finland has a five string fretted version (it was the first Ruokangas made with that system) and he says it works beatifully.

